If your radiators have cold spots or are making gurgling sounds, they probably need bleeding. It’s a straightforward process:
Turn off your oil central heating system and allow your radiators to cool down before you start. Put a towel and container underneath the bleed valve, which is usually located on the top of the radiator in the left or right corner opposite the thermostat.
Open the valve with the radiator bleed key or a screwdriver and turn slowly anti-clockwise. You’ll hear a hissing sound which is the air escaping – when water starts to come out, close the valve.
Work round your home, bleeding each radiator one by one.
Then all that’s left to do is turn your heating back on, check your radiators are warming up properly, and check your heating oil boiler pressure as bleeding radiators can sometimes lower the pressure in your system.